1. Field of the Invention
The present invention relates to a seat adjusting device adapted to adjust the position of the seat in its longitudinal direction, and particularly to a mechanically-driven seat adjusting device using a motor to effect such longitudinal seat adjustment, which is used for a power seat.
2. Description of the Prior Art
With the recent developments in an automobile or vehicle seat, increased attention has been paid to providing an electrically adjustable seat structure generally known as a power seat. Various types of the power seats have been proposed and put to a practical use. In particular, the power seat constructed for fore-and-aft adjustments of the seat position, is equipped with a seat adjusting device comprising a slide rail and a motor for causing the sliding motion of the seat in its longitudinal direction.
A conventional seat adjusting device of this kind used for the power seat is known from the Japanese Utility Model Publication No. 57-47225, for example. According to this prior art, the seat adjusting device per se is composed of a lower rail fixed to a floor of an automobile and an upper rail fixed to a seat, both of those two rails being slidably engaged together, and further a slide drive mechanism provided in the space defined between the upper and lower rails. The slide drive mechanism consists generally of a lead male screw rotatably journalled at the upper rail along the longitudinal direction of the latter, and a female screw block fixed on the lower rail, the female screw block being partially threadedly engaged with the lead male screw, and a gear box for transmitting a rotational driving force of a motor to the lead male screw. Hence, with the motor at work, the lead male screw is caused to rotate, thereby causing the sliding movement of the upper rail along the lower rail by virtue of the female screw block being fixed on the lower rail, so as to permit adjustment of the seat position in its longitudinal direction with respect to the floor of automobile.
However, in such prior art, the above-mentioned slide drive mechanism is bodily incorporated in the space defined between the upper and lower rails, which has created a negative aspect in the assembly of the seat adjusting device: annoying steps of fitting the component members, and consequent time-consuming, non-efficient procedures for completing the assembly. Moreover, such bodily incorporation of the slide drive mechanism within the upper and lower rails requires a wider space therebetween, resulting in an undesired great cross-sectional dimensions of the two rails, and thus increasing the whole dimensions of the seat adjusting device. Consequently, the prior art seat adjusting device has not been adaptable for use in a small automobile with low ceiling, having left unfavorable drawbacks.